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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN399"
>4.3. The <TT
CLASS="FILENAME"
>/etc</TT
> directory</A
></H1
><P
>The <TT
CLASS="FILENAME"
>/etc</TT
> directory contains a lot
	of files.  Some of them are described below.  For others, you
	should determine which program they belong to and read the manual
	page for that program.	Many networking configuration files are
	in <TT
CLASS="FILENAME"
>/etc</TT
> as well, and are described in the
	<I
CLASS="CITETITLE"
>Networking Administrators' Guide</I
>.

	<DIV
CLASS="GLOSSLIST"
><DL
><DT
><B
><TT
CLASS="FILENAME"
>/etc/rc</TT
> or 
<TT
CLASS="FILENAME"
>/etc/rc.d</TT
> or 
<TT
CLASS="FILENAME"
>/etc/rc?.d</TT
></B
></DT
><DD
><P
>Scripts or directories of scripts
		to run at startup or when changing the run level.
		See <A
HREF="init.html"
>Chapter 9</A
> for further
		information.  </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/passwd</TT
></B
></DT
><DD
><P
>The user database, with fields giving the
		username, real name, home directory, encrypted password, and
		other information about each user. The format is documented
		in the <B
CLASS="COMMAND"
>passwd</B
> manual page.  The encrypted
		passwords are much more commonly found in the
		<TT
CLASS="FILENAME"
>/etc/shadow</TT
> these days.  This means
		that almost everything about the user
		<EM
>except</EM
> the password is stored in the
		<TT
CLASS="FILENAME"
>passwd</TT
> file.  History and convention
		make a name change undesirable.
		</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/fdprm</TT
></B
></DT
><DD
><P
>Floppy disk parameter table.
		Describes what different floppy disk formats look
		like.  Used by <B
CLASS="COMMAND"
>setfdprm</B
>.  See the
		<B
CLASS="COMMAND"
>setfdprm</B
> manual page for more
		information.  </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/fstab</TT
></B
></DT
><DD
><P
>Lists the filesystems mounted automatically
		at startup by the <B
CLASS="COMMAND"
>mount -a</B
> command (in
		<TT
CLASS="FILENAME"
>/etc/rc</TT
> or equivalent startup file).
		Under Linux, also contains information about swap areas used
		automatically by <B
CLASS="COMMAND"
>swapon -a</B
>.  See <A
HREF="x1298.html#MOUNT-AND-UMOUNT"
>Section 6.8.5</A
> and the <B
CLASS="COMMAND"
>mount</B
>
		manual page for more information.  Also
		<TT
CLASS="FILENAME"
>fstab</TT
> usually has its own manual page in
		section 5. </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/group</TT
></B
></DT
><DD
><P
>Similar to <TT
CLASS="FILENAME"
>/etc/passwd</TT
>,
		but describes groups instead of users.  See the
		<TT
CLASS="FILENAME"
>group</TT
> manual page in section 5 for more
		information. </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/inittab</TT
></B
></DT
><DD
><P
>Configuration file for
		<B
CLASS="COMMAND"
>init</B
>.  </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/issue</TT
></B
></DT
><DD
><P
>Output by <B
CLASS="COMMAND"
>getty</B
> before
		the login prompt.  Usually contains a short description or
		welcoming message to the system.  The contents are up to
		the system administrator.  </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/magic</TT
></B
></DT
><DD
><P
>The configuration file
		for <B
CLASS="COMMAND"
>file</B
>.  Contains the
		descriptions of various file formats based on
		which <B
CLASS="COMMAND"
>file</B
> guesses the type of
		the file.  See the <TT
CLASS="FILENAME"
>magic</TT
> and
		<B
CLASS="COMMAND"
>file</B
> manual pages for more information.
		</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/motd</TT
></B
></DT
><DD
><P
>The message of the day, automatically
		output after a successful login.  Contents are up to the
		system administrator.  Often used for getting information
		to every user, such as warnings about planned downtimes.
		</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/mtab</TT
></B
></DT
><DD
><P
>List of currently mounted filesystems.
		Initially set up by the bootup scripts, and updated
		automatically by the <B
CLASS="COMMAND"
>mount</B
>
		command.  Used when a list of mounted filesystems is
		needed, e.g., by the <B
CLASS="COMMAND"
>df</B
> command.
		</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/shadow</TT
></B
></DT
><DD
><P
>Shadow password file on systems with shadow
		password software installed. Shadow passwords move the
		encrypted password from <TT
CLASS="FILENAME"
>/etc/passwd</TT
>
		into <TT
CLASS="FILENAME"
>/etc/shadow</TT
>; the latter is not
		readable by anyone except root.  This makes it harder to
		crack passwords.  If your distribution gives you a choice
		(many do) of whether or not to use shadow passwords then you
		are highly recommended to do
		so.</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/login.defs</TT
></B
></DT
><DD
><P
>Configuration file for the
		<B
CLASS="COMMAND"
>login</B
> command.  The
		<TT
CLASS="FILENAME"
>login.defs</TT
> file usually has a manual
		page in section 5. </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/printcap</TT
></B
></DT
><DD
><P
>Like <TT
CLASS="FILENAME"
>/etc/termcap</TT
>, but
		intended for printers.  However it uses different syntax.
		The <TT
CLASS="FILENAME"
>printcap</TT
> has a manual page in
		section 5. </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/profile</TT
>, 
<TT
CLASS="FILENAME"
>/etc/csh.login</TT
>, 
<TT
CLASS="FILENAME"
>/etc/csh.cshrc</TT
></B
></DT
><DD
><P
>Files executed at login or startup time
		by the Bourne or C shells.  These allow the system
		administrator to set global defaults for all users.
		See the manual pages for the respective shells.
		</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/securetty</TT
></B
></DT
><DD
><P
>Identifies secure terminals, i.e., the
		terminals from which root is allowed to log in. Typically
		only the virtual consoles are listed, so that it becomes
		impossible (or at least harder) to gain superuser privileges
		by breaking into a system over a modem or a network.  Do not
		allow root logins over a network.  Prefer to log in as an
		unprivileged user and use <B
CLASS="COMMAND"
>su</B
> or
		<B
CLASS="COMMAND"
>sudo</B
> to gain root
		privileges.</P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/shells</TT
></B
></DT
><DD
><P
>Lists trusted shells.  The
		<B
CLASS="COMMAND"
>chsh</B
> command allows users to change
		their login shell only to shells listed in this file.
		<B
CLASS="COMMAND"
>ftpd</B
>, the server process that provides
		FTP services for a machine, will check that the user's
		shell is listed in <TT
CLASS="FILENAME"
>/etc/shells</TT
>
		and will not let people log in unless the shell is
		listed there.  </P
></DD
><DT
><B
><TT
CLASS="FILENAME"
>/etc/termcap</TT
></B
></DT
><DD
><P
>The terminal capability database.
		Describes by what ``escape sequences'' various terminals
		can be controlled.  Programs are written so that instead
		of directly outputting an escape sequence that only
		works on a particular brand of terminal, they look up
		the correct sequence to do whatever it is they want to
		do in <TT
CLASS="FILENAME"
>/etc/termcap</TT
>.  As a result
		most programs work with most kinds of terminals.
		See the <TT
CLASS="FILENAME"
>termcap</TT
>, curs_termcap,
		and <TT
CLASS="FILENAME"
>terminfo</TT
> manual pages for
		more information.  </P
></DD
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